This invention relates to oil well production equipment and, in particular, to artificial lift installations.
A common method of achieving artificial lift in an oil well involves the use of an insert pump which is installed at a prescribed depth within the production tubing. Depicted in FIG. 1 is a conventional pump 10 which has been lowered into a conventional production tubing 12 by means of sucker rods (not shown). The production tubing comprises a plurality of tube segments 12A, 12B, 12C interconnected by tubing collars 14, 16. The tube segment 12B constitutes a seating nipple which is adapted to receive a hold-down projection 18 of the pump. The hold-down projection, which is of cylindrical shape, carries a plurality of elastic seal rings or cups 20 which seal against an inner bore 22 of the seating nipple 12B.
The pump further includes a no-go ring 24 fixed at the top of the hold-down projection. The no-go ring 24 has an outer diameter which is larger than the outer diameter of the pump barrel 25, and which is appreciably larger than the diameter of the bore 22 of the seating nipple to limit the downward travel of the pump by abutting against the top of the seating nipple 12B.
The pump is installed by being lowered such that the hold-down projection enters the seating nipple 12B, and the no-go ring 24 abuts the top of the seating nipple 12B, providing a positive indication that the pump 10 is seated on the seating nipple. The pump remains connected in that fashion during the period in which it pumps fluid from the well. When it becomes necessary to remove the pump from the well for replacement or repair, the pump is pulled up by the sucker rods. Eventually the seal cups are pulled from the seating nipple. This enables fluid in the tubing to by-pass the seal cups and seek a hydraulic balance inside and outside of the tubing. Thereafter, the pump is raised from the tubing 12.
It sometimes occurs, however, that the pump becomes stuck within the seating nipple 12B, requiring that the tubing be raised, at considerable time and expense.
It is the belief of the present inventor that such sticking of the pump results from the accumulation of debris such as sand and scale S, for example, within an annular space 26 formed between a cylindrical inner surface 27 of the tubing collar 14 and a cylindrical outer surface of the pump, as depicted in FIG. 3. The surface 27 is disposed between threaded sections 29, 31 of the tubing collar 14. The accumulated debris moves upwardly with the pump and becomes wedged within a restriction 30 formed between the tubing 12A and the outer periphery of the pump, thereby inhibiting further raising of the pump.
It would, therefore, be desirable to provide a tubing section which enables the pump to be removed.